How to Identify Pulse Circuit Diagram

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Summary

There are a wide range of electrical pulse shape, sch as a rectangular, triangular, zigzag, bell, staircase and spire-shaped, the most representative of which is the rectangular pulse. Pulse circuit is designed to produce electrical pulses and electric pulse amplification, transformation and shaping of the circuit. Household appliances’ timer, alarm, electronic switches, electronic watches, electronic toys and electronic medical devices, etc, are using pulse circuits.

In electronic circuits, power supply circuits, amplification circuits, oscillation and modulation circuits are called analogue electronic circuits because they process and handle continuously varying analog signals. Digital electronic circuits is another category of electronic circuits. The object it processes is a discontinuous digital signal. Digital electronic circuits can be divided into pulse circuits and digital logic circuits, which deal with non-continuous pulse signal. Pulse circuit is designed to produce electrical pulses and electric pulse amplification, transformation and shaping of the circuit. Household appliances’ timer, alarm, electronic switches, electronic watches, electronic toys and electronic medical devices, etc, are using pulse circuits.

There are a wide range of electrical pulse shape, sch as a rectangular, triangular, zigzag, bell, staircase and spire-shaped, the most representative of which is the rectangular pulse. To illustrate the characteristics of a rectangular pulse can adapt pulse amplitude Um value, pulse period T or frequency f, pulse front tr, pulse trailing edge tf and pulse width tk. If the width of a pulse t k = 1 / 2T, that means it is a square wave.

The biggest difference between the pulse circuit and amplified oscillation circuit, in other words, pulse circuit is characterized by: the transistor in the pulse circuit is working in the switch state. In most cases, the transistor is operating in the saturation or cut-off of the characteristic, so the pulse circuit is sometimes called the switching circuit. From the use of the transistor, It can also be seen at higher frequencies the special switch, such as 2AK, 2CK are used. Only when the operating frequency is low, we use the general kinds of the transistor like DK, 3AK-type tube.

Take the most commonly used inverter circuit (Figure 1) among pulse circuit as an example.Ffrom the circuit form point of view, it is very similar to co-emission amplifier circuit. In the amplifier circuit, the base resistor R b2 is connected to the positive supply to obtain the base bias. But in this circuit, in order to ensure a reliable circuit cut-off, R b2 is connected to a negative power supply, and the value of R b1 and R b2 are calculated by the requirement of when transistor-dependent can deep into the saturation region reliably. Not only, in order to make the transistor switching faster, the base is also added acceleration capacitor C, The leading edge generates a positive spike to allow the transistor to quickly turn on and saturate. A negative spike is generated at the trailing edge of the transistor to rapidly bring the transistor to the off state. In addition to the emitter output is a special case, the pulse circuit transistors are working in the switch state, which is a specific feature.

Figure 1 inverter circuit

Another characteristic of the pulse circuit is that there must be a capacitor (with less inductance) as the key component. Pulse generation, waveform transformation are inseparable from the capacitor charge and discharge.

II.Multivibrator Pulse Generator

There are a variety of uses for the pulse. There are control pulses for switching the circuit, clock pulses for the overall effect of the commander, counting pulses for counting, trigger pulses for starting the trigger, and so on. No matter what the pulse is generated by the pulse signal generator, and most of them are short pulses or rectangular pulses into the prototype into. Because the rectangular pulse contains a wealth of harmonics, so the pulse signal generator is also called self-excited multivibrator or multi-harmonic oscillator. If the door is used as a metaphor, multivibrator output when the closed state of the multivibrator can be compared to the hotel's automatic revolving door, it does not need people to promote, but always open and close the door.

2.1 Integrated base coupled multivibrator

Figure 2 is a typical set of discrete components based on the coupling of multivibrator. It consists of two transistor inverter RC circuit cross-coupled into a positive feedback circuit. Two capacitors charge and discharge alternately to turn on and off the two tubes, keeping the circuit turning from one state automatically to another state, results for the formation of self-excited oscillation. From point A or point B can get the output pulse. When R b1 = R b2 = R, C b1 = C b2 = C, the output is a square wave with a magnitude close to E with a pulse period of T = 1.4 RC. If both sides are not symmetrical, the output is a rectangular pulse

Figure 2 a typical set of discrete components based on the coupling of multivibrator

The 555 is an integrated circuit that combines the features of digital and analog circuits and is widely used in some time-dependent circuits. Because the peripheral circuit is simple, so the cost is very low! Today talk about how to use 555 to design multivibrator.

The following figure 3 is a more practical multivibrator circuit, the core component is 555, the simulation waveform as shown in the lower right corner, physical measurement of the waveform as shown below oscilloscope waveform!

Figure 3 a more practical multivibrator circuit

CB555 function table is as following:

Input

Output

RD

V11

V12

V0

TD state

0

*

*

low

Turn on

1

>2Vcc/3

>Vcc/3

low

Turn on

1

<2Vcc/3

>Vcc/3

constant

constant

1

<2Vcc/3

<Vcc/3

high

Turn off

1

>2Vcc/3

<Vcc/3

high

Turn off

The main design point is that the use of capacitor C1 charge and discharge to get different levels, 555 inside the two compared in different levels of flip, and then provide input to the RS flip-flop, which outputs a resonant square wave. The output frequency, can be calculated using the following formula: 1.44 / (R1 +2 R2) C1.

Here is a video about 555 Pulse Generator Circuit:

This video shows a simple 555 pulse generator is used in flashing LEDs and pulse generator

for stepper motors. You could use a manual stepper driver in a CNC machine etc.

2.3 RC ring oscillator

Figure 4 shows a typical RC ring oscillator. It uses an odd number of doors, connected to form a closed loop, there RC delay circuit in the loop. The figure RS is the protection of resistance, R and C delay circuit components, their values determine the pulse period. Output pulse period T = 2.2RC. If you replace the potentiometer with R, it becomes a multivibrator with adjustable pulse frequency. Because of this circuit is simple and reliable, easy to use, wide frequency range, and can be changed from several hertz to several megahertz, it is widely used.

Figure 4 a typical RC ring oscillator

Detail

III.Circuit Diagram of Pulse Transformer

Pulse at work sometimes need to transform the waveform or amplitude, such as the rectangular pulse into a triangular wave or spike, etc., with this function circuit is called transform circuit. Pulses can cause distortion during transmission and are therefore often trimmed with imprecise waveforms to make them look new. Circuits with this function are called plastic circuits.

3.1 Differential pulse transformer circuit

Differential circuit is the most commonly used pulse circuit pulse transform circuit, which is very similar to the RC coupling circuit in the amplifier circuit, shown in Figure 5. When the circuit time constant ┱ = RC << t k, the input rectangular pulse, the capacitor charge and discharge very fast, the output can be a pair of spikes. The leading edge of the input pulse outputs a positive spike and the trailing edge of the input pulse outputs a negative spike. This type of spike is often used as a trigger or count pulse.

Figure 5 RC coupling circuit

3.2 Integral circuit

Replacing R and C in Figure 5 and making ┱ = RC >> tk, the circuit becomes an integrating circuit, see Figure 6. When the input rectangular pulse, the capacitor charge and discharge is very slow, the output is a series of lower amplitude approximate triangular pulse wave.

Figure 6 integrating circuit

3.3 Limiter

A circuit that limits the pulse amplitude is called a limiter or a chopper. Figure 7 is an upper limit circuit composed of a diode and a resistor. It can cut off the input positive pulse. If you reverse the diode, it becomes cut off the negative pulse of the lower limit circuit.

Figure 7 is an upper limit circuit composed of a diode and a resistor

Non-linear devices such as bipolar or triode can be used to form a variety of limiter, or transform the waveform (such as the input pulse into a square wave, trapezoidal wave, spike, etc.), or pulse shaping (such as the input level Uneven pulse series flattened into a neat series of pulses, etc.).

3.4 Clamp

A circuit that maintains the pulse voltage at a constant value and keeps the waveform constant is called a clamper. It is also a kind of plastic circuit. For example, the transmission of television signals will cause distortion. In order to recover the pulse waveform, the clamp circuit is used in the receiver to clamp the top of the waveform at a fixed level.

Figure 8, the output of the inverter there is a clamp diode VD. Without this diode, the output pulse high should be 12 volts, a clamp diode is now added and the output pulse high is clamped to 3 volts.

Figure 8 inverter there is a clamp diode VD

In addition, such as inverter, emitter output circuit also has the "whole as new" role, can also be considered plastic circuit.

Bistable circuit with memory function Multivibrator output is always high and low when the conversion, so it is also called no steady-state circuit. Another bistable circuit is absolutely different. Bistable circuit has two outputs, they are always in the opposite state: one is high, the other must be low. It is characterized by the absence of external trigger, the output state can remain unchanged. So it is often used as a unitary circuit for registering binary digits.

3.5 Integrated base coupling bistable circuit

Figure 9 is a set of discrete components set base-coupled bistable circuit. It consists of a pair of resistors cross-coupled inverter composition. For example, when the VT1 tube is saturated, the VT2 tube is turned off. At this time, the A point is at a low level and the B point is at a high level. If there is no external trigger signal, it will remain unchanged. If the high level indicates the digital signal "1" and the low level indicates "0", then the bistable circuit can be assumed to have the digital signal "1" stored at the B terminal.

Figure 9 a set of discrete components set base-coupled bistable circuit

The base of the circuit is added differential circuit. If a negative pulse (known as a trigger pulse) is added to the base of VT1, the base potential of VT1 will drop. Due to the positive feedback, VT1 will quickly turn from saturation to end and VT2 will turn from saturation to saturation. The bistable circuit is then flipped to "1" on the A side and "0" on the B side, which will be maintained.

3.6 Trigger pulse triggering method and polarity

Bistable circuit trigger circuit trigger pulse polarity and the choice of more complex. From the trigger mode, because of the DC trigger (potential trigger) and AC trigger (edge ??trigger) of the difference, so the trigger circuit in different forms. From the pulse polarity, but also with the transistor polarity, the trigger pulse is added to which tube (saturated tube or tube), which pole (base or collector) and change. In practical applications, because the differential circuit can easily get a sharp pulse, the trigger is better, so the use of AC trigger mode. The location of the trigger pulse is mostly applied to the base of the saturated tube. Therefore, the use of NPN tube bistable circuit is added negative pulse, and PNP tube bistable circuit is a positive pulse.

3.7 Integrated flip-flop

In addition to integrated flip-flop with discrete components, but also can be integrated circuit composed of bistable circuit. However, in fact, there are currently a large number of integrated bistable flip-flop products to choose from, such as R-S flip-flops, D flip-flops, JK flip- The direct use of ready-made products.

IV.Circuit Diagram Pluse Delay

There are 2 non-steady-state transient state without steady-state, bistable circuit has 2 steady-state without temporary steady-state. The third circuit commonly used in pulse circuits is a monostable circuit, which has a steady state and a temporary steady state. If you also use the door as a metaphor, monostable circuit can be seen as a spring door, usually it is always off, "off" is its steady state. When someone push it or pull it when the door opens, but due to the elastic effect, the door quickly and automatically shut down, restored to its original state. So "open" is its temporary homeostasis. Monostable circuits are often used as timing, delay control, and shaping.

4.1 Integrated base-coupled monostable circuit

Figure 10 shows a typical set of base-coupled monostable circuits. It is also a positive feedback circuit formed by the two-stage inverter cross-coupled. Half of it is similar to a multivibrator, and the other half is similar to a bistable circuit, plus it also has a differential trigger circuit, so it is conceivable that it is a combination of half a nonstable circuit and half a bistable circuit, and it should There is a steady state and a temporary steady state. Usually it is always a tube (VT1) saturation, the other tube (VT2) cut-off, and this is its steady state. When a trigger is input, the circuit flips to another state, but this state lasts for a short time and quickly returns to its original state. The transient time of the circuit is determined by the values of delay elements R and C: t t = 0.7RC.

Figure 10 shows a typical set of base-coupled monostable circuits

4.2 Integrated monostable circuit

Integrated gate can also form a monostable circuit. Figure 11 is a differential type monostable circuit, which uses two non-gate cross-connect, the door 1 is output to the door 2 is coupled by a differential circuit, the door 2 is output to the door 1 is directly coupled to the trigger pulse is applied to the other door 1 Input UI. Its temporary steady state time is t t = (0.7 ~ 1.3) RC.

Figure 11 is a differential type monostable circuit

Analysis

V.Pulse Circuit Analysis

Pulse circuit is characterized by that its input and output are pulse when working in the switch state. So during the analysis, we should seize the key to distinguish between the primary and secondary circuits. First identify the main circuit functions, and then analyze the role of auxiliary circuits.

Grasp the key from the circuit structure to find similarities and differences. The basic principle of the three base unit circuits based on the base coupling method is described above. Both of them are formed by the double-tube inverter as the positive feedback circuit, which is their common point. However, the detailed analysis shows that they all have their own characteristics. Although the unsteady and bistable circuits all have a symmetrical form, the unsteady circuit uses capacitive coupling and the bistable is directly coupled with a resistor (sometimes in parallel with an accelerating capacitor, and the capacity is generally very large Small); and bistable circuits generally have a trigger circuit (double-ended or single-ended trigger); monostable circuit is well recognized that it is asymmetric, both bistable and monostable form. Such an analysis, the three circuits are very different.

In Pulse circuit, the pulse generation, transformation and shaping are related to capacitor’s charge and discharge. The circuit time constant value as the value of R and C which determines the nature of the circuit has a very important significance. It is particularly important.

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